As we have mentioned in the study on the absorption spectra of complex, the pH value of extraction for Cd was different from some conventional works in alkaline solution, which led to a different maximum absorption wavelength. This could be one of the key factors contributed to the high sensitivity and enhancement factor. The proper acidity of copper, from the results of Fig. 6, was 9.2 by using ammonium chloride ammonia buffer solution and masking reagent-EDTA. Hereby, pH 3.0 was selected for cadmium while pH 9.2 was chosen for copper in the further experiments.